JP3099863B2 - Aperture control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aperture control circuit for adjusting an aperture for obtaining an optical image of a subject with an optimum amount of light with a simple structure.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram for explaining a conventional aperture control circuit.

In a video camera, a camera section having an optical system for capturing an optical image is provided with an aperture control circuit for keeping the amount of light incident on the optical system constant. The aperture control circuit, as shown in FIG. 2, an optical system 1 for capturing an optical image, a diaphragm mechanism 2 for adjusting the amount of light of the optical image captured by the optical system 1, and a predetermined light amount adjusted by the diaphragm mechanism 2. A CCD 3 for photoelectrically converting an optical image into a video signal, a signal processing circuit 4 for performing predetermined signal processing to be described later on the video signal output from the CCD 3, and an A / A for converting the video signal output from the signal processing circuit 4 into a digital signal D converter 5, light amount data calculation circuit 6 for calculating the light amount of the optical image from the digital video signal output from A / D converter 5, the output result of light amount data calculation circuit 6, and the position from aperture mechanism 2 described later A control amount calculation unit 7 for calculating a control amount for driving the aperture mechanism 2 from the information, a bit rate conversion unit 9 for converting the control amount calculated from the control amount calculation unit 7 to a predetermined bit rate,
A D / A converter 10 for converting the control amount converted into a predetermined bit by the bit rate conversion unit 9 into a control signal,
A drive circuit 11 for controlling the driving of the diaphragm mechanism 2 based on a control signal output from the converter 10, a diaphragm position detecting means 12 for detecting a diaphragm position of the diaphragm mechanism 2, and a position information detected by the diaphragm position detecting means 12 An element amplifier 13 for amplifying the signal to a predetermined signal level;
It is composed of

Although not shown here, the signal processing circuit 4 separates the video signal supplied from the CCD 3 into a luminance signal and a color difference signal through a frequency band filter.
Each performs a predetermined signal processing. Luminance signal is LP not shown
After passing through an F (low-pass filter), the electric signal that has been photoelectrically converted by the gamma correction circuit is corrected and supplied to the vertical and horizontal contour correction circuits. After passing through a BPF (Band Pass Filter) centered on the carrier frequency, the color difference signal is demodulated for each scanning line by a synchronous detection circuit (not shown), and the above-described luminance signal is added to generate a line-sequential signal. The color difference signal from which the above-mentioned luminance signal has been subtracted via a white balance and gamma correction circuit is synchronized by a 1H delay line. Then, a luminance signal obtained by adding the above-mentioned luminance signal and the synchronizing signal and a color difference signal are respectively generated, and this luminance signal is supplied to the A / D converter 5.

The video signal obtained by the signal processing circuit 4 is supplied to a not-shown display device (viewfinder, monitor, etc.) or a VTR recording system.

The luminance signal converted into a digital signal by the above-mentioned A / D converter 5 is supplied to a light quantity data calculation circuit 6, and the quantity of light (object) irradiated onto the element surface of the CCD 3 by the light quantity data calculation circuit 6 The information signal based on the luminance information is supplied to the control amount calculation unit 7.

As described above, the control amount calculating section 7 calculates a control signal based on this information signal and aperture position information detected by aperture position detecting means 12 which will be described later. It is supplied to the drive circuit 11 via the D / A converter 10. The drive circuit 11 includes the D / A converter 1
A drive current is generated based on the control signal converted into an analog signal via the control signal 0 and supplied to the aperture mechanism 2. That is, for example, if the amount of light illuminated on the element surface of the CCD 3 by the information signal exceeds a predetermined amount, the control amount calculation unit 7 determines the information signal of the amount of light at that time and the current aperture of the aperture mechanism 2. A control signal for closing the aperture mechanism 2 is calculated based on the aperture position information indicating the state.

The stop mechanism 2 stops light incident from the optical system 1 on the basis of the drive current output from the drive circuit 11, and detects a stop position of the stop mechanism 2 at this time. The detecting mechanism 12 controls the aperture mechanism 2
The control amount calculation unit 7 detects an aperture position corresponding to the drive amount of the control unit 7 through an element amplifier 13 that amplifies the detection result to a predetermined amount and an A / D converter 14 that converts the amplified detection result into a digital signal. To supply.

Thus, the amount of light incident on the camera section of the video camera can be always kept constant by the aperture control circuit.

[0010]

However, in the above-described aperture control circuit, the ratio of the change in the aperture position of the aperture mechanism 2 to the change in the amount of light of the subject is non-linear.
For example, the aperture mechanism 2 is a mechanism that determines the area of the optical path of the incident light from the above-described aperture position information and limits the amount of light of the subject incident on the CCD 3. In other words, since the diaphragm amount corresponding to the area of the optical path of the incident light which is two-dimensional is obtained from the fluctuation of the diaphragm position which is one-dimensional, the change of the diaphragm amount with respect to the change of the diaphragm position becomes nonlinear, Is smaller; for example, the aperture state when the amount of light of the subject is large). Conversely, the change in the aperture position with respect to the change in the amount of light of the subject becomes smaller as the aperture becomes smaller.

For example, when the subject brightness (the amount of light of the subject) changes twice, the aperture is open (the area of the optical path of the incident light is increased) in the state where the subject brightness is low. In order to change the area of the optical path of light by half, the stop position is largely moved. In addition, when the subject brightness is high, the aperture is originally in a small aperture state, so that the area of the optical path of the incident light is changed to half, so that the aperture position is moved small.
At this time, the output of the diaphragm position detecting means 12 obtained according to the change of the diaphragm position becomes smaller.

For this reason, when the amount of light of the subject is high,
There is an inconvenience that it is difficult to accurately control the aperture mechanism 2 according to the output of the small aperture position detecting means.

Since the aperture position detecting means 12, the element amplifier 13 and the A / D converter 14 have noise on the circuit irrelevant to the aperture position, the aperture position detecting means 12
However, when the output of the aperture becomes small, there is a problem that the reliability of the information on the aperture position becomes low due to the influence of noise.

Since the quantization accuracy and the resolution of the A / D converter 14 are finite, the transmission accuracy of the aperture position information output from the aperture position detecting means 12 depends on the A / D converter 1.
There was an inconvenience of being affected by the performance of No. 4.

Also, due to the above-mentioned inconveniences and problems, the higher the brightness of the subject, the lower the quantization accuracy of the A / D converter 14, and when the brightness exceeds a certain level, the output of the A / D converter 14 becomes A Since the resolution is lower than the resolution of the / D converter 14, there is a problem that the aperture position cannot be detected.

[0016]

Accordingly, the present invention provides the following configuration in order to solve the above-mentioned problems.

An aperture mechanism 2 for taking in an optical image to be captured and adjusting the light quantity of the optical image, and means 6 for calculating information on the light quantity of the optical image from a video signal obtained by capturing the optical image. A control means for controlling the driving of the diaphragm mechanism 2 based on an output result of the means 6 for calculating information on the light quantity of the optical image; A diaphragm control circuit comprising: filter means 8 for generating and outputting a control amount corresponding to a diaphragm position of the diaphragm mechanism 2 based on an output result of the means 6 for calculating information.

[0018]

FIG. 1 is a block diagram for explaining an embodiment of the aperture control circuit according to the present invention. Hereinafter, an aperture control circuit according to the present invention will be described with reference to the drawings. The same components as those described above are denoted by the same reference numerals, and description thereof will be omitted.

An aperture control circuit according to the present invention captures an optical image to be picked up and adjusts a light amount of the optical image.
And a means (light amount data calculation circuit) 6 for calculating information on the light amount of the optical image from a video signal obtained by capturing the optical image, based on the output result of the light amount data calculation circuit 6. Control means (bit rate converter 9, D / A converter 10, driving circuit 11) for controlling the driving of the diaphragm mechanism 2 and the diaphragm position of the diaphragm mechanism 2 based on the output result of the light quantity data calculating circuit 6. And a filter means (digital filter) 8 for generating and outputting the controlled variable.

Now, an aperture control circuit according to the present invention will be described. As shown in FIG. 1, an optical image of a subject incident through an optical system 1 and an aperture mechanism 2 is photoelectrically converted by a CCD 3 into a video signal. The signal is supplied to the signal processing circuit 4.

The video signal that has been subjected to the above-described signal processing by the signal processing circuit 4 is supplied to a light quantity data calculation circuit 6 via an A / D converter 5, and the light quantity of an optical image is calculated. The output result of the light amount data calculation circuit 6 is supplied to a control amount calculation unit 7, which calculates a control amount for driving the aperture mechanism 12.

The control amount calculated by the control amount calculator 7 is supplied to a digital filter (filter means) 8 and a bit rate converter 9 which are essential parts of the present invention.

The digital filter 8 comprises, for example, a digital multiplier / adder, a digital divider, and a unit delay operation element. That is, the digital filter 8 has the input X
Transfer function H for obtaining, for example, output Y (Z) from (Z)
This is filter means having the characteristic represented by (Z).

Here, the control amount of the aperture mechanism 2 calculated by the control amount calculator 7 and the aperture position of the aperture mechanism 2 relatively correspond. That is, for example, when the light amount of the optical image is large, the diaphragm mechanism 2 is at the diaphragm position for reducing the amount of light, and when the light amount of the optical image is small, the diaphragm mechanism 2 is at the diaphragm position opened to take in a large amount of light. At this time, the diaphragm position information of the diaphragm mechanism 2 corresponding to the voltage obtained according to the change in the light amount of the optical image (for example, the voltage obtained by RC integration of the video signal captured by the light amount data calculation circuit 6) is obtained. Can be

That is, the amount of change in the diaphragm position information according to the voltage transient characteristic is determined, and the control amount of the diaphragm mechanism 2 calculated by the control amount calculator 7 is obtained according to the voltage transient characteristic. The aperture position of the aperture mechanism 2 is determined based on the output result of the calculation circuit 6. Therefore, by setting the transfer function of the digital filter 8 to a transfer function equivalent to converting the control amount of the stop position supplied to the stop mechanism 2 into the stop position information, the digital filter 8 can operate the light amount data calculation circuit 6. The control amount equivalent to the stop position of the stop mechanism 2 can be output based on the output result of.

The digital filter 8 is configured to set a transfer function equivalent to obtaining diaphragm position information from the control amount of the diaphragm position supplied to the diaphragm mechanism 2 as described above. For example, a low-pass filter of an arbitrary order is configured according to a signal frequency band supplied to the digital filter 8 and a mechanism to be controlled (including a drive circuit). Alternatively, it is constituted by a combination of low-pass filters of any order.

In this manner, the digital filter 8 can supply an information signal equivalent to the above-described aperture position information to the control amount calculation unit 7 based on the control amount output from the control amount calculation unit 7, The calculation unit 7 can calculate a control signal for controlling the aperture mechanism 2.

The control signal calculated by the control amount calculation unit 7 is converted into predetermined bits by the bit rate conversion unit 9 as described above, and is passed through the D / A converter to the drive circuit 11.
Supplied to Then, the drive circuit 11 drives the diaphragm mechanism 2 based on the supplied control signal, and sets the amount of light of the optical image to a predetermined amount.

In this way, by using the digital filter 8 as described above, an information signal having a transient characteristic equivalent to the aperture position information is obtained from the control signal calculated by the control amount calculating section 7. 8
Can be used in the control amount calculator 7 as aperture position information.

At this time, the output signal of the digital filter 8 is supplied to the aperture position detecting means and the element amplifier 1 as described above.
Since there is no noise on the circuit irrelevant to the aperture position, which occurs in the A / D converter 3 and the A / D converter 14, the detection of the aperture position particularly in a small aperture area is improved. That is, even when the brightness of the subject is relatively high and the aperture mechanism 2 is in the small aperture state, the recognition accuracy of the aperture position information corresponding to the change in the aperture position is improved.

The output signal of the digital filter 8 is A
Since it does not pass through the / D converter 14, the quantization accuracy and transmission accuracy of the aperture position information are not affected by the performance of the A / D converter 14. Further, the control signal output from the control amount calculation unit 7 is supplied to the digital filter 8 at the same bit rate, and an information signal equivalent to the aperture position information obtained through the A / D converter 14 is obtained. As mentioned above, A /
The bit rate of the aperture position information is not deteriorated as compared with the aperture position information obtained via the D converter 14. That is, since the apparent resolution is improved, the recognition accuracy of the aperture position information corresponding to the change in the aperture position is improved even when the brightness of the subject is high.

Further, since the aperture position information can be obtained with high precision by the digital filter 8, it can be applied to one of means for correcting the nonlinear characteristic of the aperture mechanism 2 almost linearly, so that the aperture position control can be simplified. (E.g., an IC of a digital filter), the transient characteristics of the drive control of the aperture mechanism 2 can be made uniform at any aperture position, and the characteristics of the entire aperture control circuit can be stably adjusted.

[0033]

As described above, according to the first aspect of the present invention, an aperture mechanism for taking in an optical image to be picked up and adjusting the amount of light of the optical image as in a conventional aperture control circuit. Means for calculating information on the light amount of the optical image from a video signal obtained by capturing the optical image, and position detecting means for detecting a stop position of the diaphragm mechanism, wherein information on the light amount of the optical image is provided. And a filter having a transfer function equivalent to the position detecting means, compared to a control having a control means for controlling the drive of the diaphragm mechanism based on an output result of the position detecting means. Since the configuration is characterized in that the output result of the filter means is used as aperture position information having transient characteristics equivalent to those of the position detection means. That is, by using the output result of the filter means, the aperture position detection means, the element amplifier, the A / A
Since there is no noise on the circuit irrelevant to the aperture position that occurs in the D converter or the like, the recognition accuracy of the aperture position information corresponding to the change in the aperture position is improved even when the brightness of the subject is high.

Further, by using the output result of the filter means, the quantization accuracy and transmission accuracy of the aperture position information are not affected by the performance of the A / D converter, and the control signal output from the control amount calculation unit is not affected. Since the bit rate is higher than the bit rate of the A / D converter, the apparent resolution is improved, and the recognition accuracy of the aperture position information corresponding to the change in the aperture position is improved.

Further, since the aperture position information can be obtained with high accuracy by using the output result of the filter means, it can be applied to one of means for correcting the nonlinear characteristic of the aperture mechanism almost linearly. Position control can be performed with a simple configuration (eg, digital filter IC integration), the transient characteristics of the drive control of the aperture unit can be made uniform for any aperture position, and the characteristics of the entire aperture control circuit can be stably adjusted. There is an effect that it becomes possible.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining one embodiment of an aperture control operation according to the present invention.

FIG. 2 is a block diagram for explaining a conventional aperture control circuit.

[Explanation of symbols]

 6 Means for calculating light amount information of an optical image 7, 9, 10, 11 Control means 8 Filter means 12 Aperture mechanism

Claims (1)

(57) [Claims] An aperture mechanism for capturing an optical image to be captured and adjusting a light amount of the optical image; and a means for calculating information on a light amount of the optical image from a video signal obtained by capturing the optical image. An aperture control circuit, comprising: a control unit that performs drive control of the aperture mechanism based on an output result of the unit that calculates information on the amount of light of the optical image; and an output of a unit that calculates information on the amount of light of the optical image. A diaphragm control circuit, comprising: filter means for generating and outputting a control amount corresponding to a diaphragm position of the diaphragm mechanism based on a result.